In recent years, the liquid crystal display device for use in a personal computer has been demanded to have higher display quality in terms of color representation, high brightness and high resolution. The liquid crystal display device is basically constituted of a liquid crystal panel and an illumination device, which is an illuminating means. The liquid crystal panel is classified to transmission type and reflection type and the transmission type liquid crystal panel has the illumination device on its rear face while the reflection type liquid crystal panel has the illumination device on its front face.
FIG. 7 is a sectional view showing a conventional transmission type liquid crystal panel. In the transmission type liquid crystal panel, as shown in FIG. 7, a polarizer 214 is incorporated between a glass substrate 210 and a glass substrate 212. Bus line is formed on the glass substrate 212. Liquid crystal 220 is sealed between the glass substrate 212 and a glass substrate 218. A color filter 224 is sandwiched between the glass substrate 218 and a glass substrate 222. A polarizer 228 is sandwiched between the glass substrate 222 and a glass substrate 226.
In the transmission type liquid crystal panel, the color filter and the liquid crystal are sandwiched between the polarizers and in the reflection type liquid crystal panel, the polarizer 214 is replaced with a reflecting plate such as a mirror. In either liquid crystal panel, when linearly polarized light passes through the liquid crystal, the phase is modulated due to its characteristic and then, it passes through the color filter and when it passes through or is intercepted, white and black representations are produced. When plural pieces of this dot are arranged, character information or image information is created. On the other hand, because the liquid crystal is a light receiving type device, the aforementioned information cannot be recognized visually on the liquid crystal alone.
To solve this problem, generally, the illumination device as an illuminating means is disposed on the rear face (back) in case of the transmission type liquid crystal panel and in case of the reflection type liquid crystal panel, it is disposed on the front face (front). Because the reflection type liquid crystal panel is illuminated by the sun light or indoor light, it does not need any illumination device under such a condition. However, unless it is located under such illumination environment, it needs the illumination device like the transmission type. The illumination device is constituted of a point light source and a light guide plate and light emitted from the point light source such as LED is entered into the light guide plate and then projected to the entire surface of the liquid crystal panel.
The LED is disposed on an end face of the light guide plate and the light guide plate is formed such that the bottom face (opposite face to light emission face) of the light guide plate has an angle. LED light leaking from the top face (light emission face) of the light guide plate due to collapse of total reflection condition is emitted through prism sheet disposed thereon. Usually, 3-4 pieces of the LEDs are used in every 2 inch size. Because no light exists between the LEDs, brightness unevenness called eye ball in Japanese language is generated particularly in the vicinity of a LED upon which the LED light impinge, the eye ball being formed such that the brightness is high on the front face of the LED while the brightness is low between the LEDs. In the vicinity of the LED, it is difficult to adjust brightness because the total reflection condition cannot be controlled well and in the vicinity of the LED, there were problems such as lower luminance is generated.
Then, for example, patent document 1(Japanese Patent Application Laid-Open (JP-A) No. 2004-006326) has disclosed art in which a prism is formed on a light emission face or an opposite face to the light emission face while rough surface (scattering face) is formed on an opposite face to the prism face in order to prevent a lower luminance in the vicinity of the LED.
However, because light is scatted by the rough surface of the light, there is a problem that entire lower luminance although brightness unevenness in the vicinity of the LED is improved.
Additionally, patent document 2(JP-A No. 2002-216530) has disclosed another art of changing the taper angle of the light emission face or the opposite face to the light emission face of the light guide plate partially to prevent a lower luminance in the vicinity of the LED.
However, there was a problem that a line appears at a position in which the taper angle changes, thereby dropping the display quality.
Further, patent document 3(JP-A No. 2003-114432) has disclosed still another art of providing a light guide plate having lens arrays on both side faces, a light polarizing device on a light emission face of the light guide plate and a light reflecting device on a face opposing the light emission face so as to ensure an appropriate emitted light distribution.